FIG. 1 illustrates an example of a conventional wireless communication system. In the example of FIG. 1, a base station 11 communicates bidirectionally with a plurality of mobile stations 13 via radio signals passing through a transmission channel 15. Such an arrangement is typical of cellular telecommunications systems and other wireless communications systems. The transmission technology can be any of a variety of conventional technologies, for example, code division multiple access (CDMA), time division multiple access (TDMA), and frequency division multiple access (FDMA).
FIG. 2 is a block diagram which illustrates an example of a conventional transceiver 21 which may be included in each of the mobile stations 13 and the base station 11 of FIG. 1. The transceiver 21 transmits radio signals over the transmission channel 15 to other communication stations, and receives radio signals via transmission channel 15 from other communication stations. The transceiver 21 includes a transmitter 17 and a receiver 19. A conventional transmitter processing apparatus at 12 provides various signals to a conventional transmit section 14 which interfaces the signals from the transmitter processing apparatus 12 to an antenna 20 that transmits corresponding radio signals over the transmission channel 15. The antenna 20 also receives radio signals from the transmission channel 15 and provides them to a receive section 16 which converts the signals received from antenna 20 into signals which are input to a conventional receiver processing apparatus at 18.
The transmitter processing apparatus at 12 produces the substantive information, that is, the message to be communicated over the transmission channel to a receiving communication station, and also provides control signals such as pilot symbols, power control information and other control signals. Substantive information, pilot symbols, power control information and other control information are also received from the transmission channel 15 and provided from receive section 16 to receiver processing apparatus 18.
The power control information or power control symbols (often referred to as TPC (Transmission Power Control) bits) are regularly transmitted in order to compensate for changes in the transmission channel between the transmitting and receiving stations, such as fading. Pilot symbols are transmitted to help the receiver estimate the channel and carry out coherent detection of received signals. The pilot symbols transmitted by the transmitter are already known in advance at the receiver, so that the receiver can evaluate channel conditions by comparing the pilot symbols actually received to the expected pilot symbols.
The pilot symbols and power control symbols constitute a significant part of the non-information signals communicated over the transmission channel. Moreover, these signals require significant transmission power. The pilot and power control symbols are conventionally transmitted either in the same physical channel as the substantive information, or in a control channel which is separate from the information channel. Both the power control and pilot symbols can be transmitted in either the uplink or downlink directions of the system illustrated in FIG. 1. In conventional CDMA systems such as specified in IS-95, up to 20% of the total transmitted power is used for pilot symbol transmission, and the power control symbols constitute up to 10% of the total symbols transmitted over the channel. These figures are typical of other conventional CDMA systems such as the "Code Division Testbed" (CODIT), and the wideband CDMA standards being developed in Japan and Europe.
FIG. 3 illustrates one example of the transmission of pilot symbols and power control symbols in the transmission channel of a wireless communications system. The illustration in FIG. 3 is an example of the transmission of pilot symbols and power control symbols over a physical channel which is separate from the physical channel used for transmission of substantive information signals. Regardless of whether the pilot symbols and power control symbols are transmitted over a separate channel or over the same channel as the substantive information signals, the present invention recognizes that any reduction in the amount of pilot symbols and/or power control symbols to be transmitted will result in a corresponding increase in available channel capacity, a corresponding decrease in required transmission power, and a corresponding decrease of interference over the transmission channel.
It is therefore desirable to provide for one or more of: increased available channel capacity; decreased transmission power; and decreased interference; while also providing for transmission and receipt of all desired pilot symbols and power control information.
The present invention provides for transmitting and receiving all desired pilot symbols and power control information while improving upon conventional systems with respect to one or more of: the required channel capacity; the required transmission power; and the transmission channel interference. This is achieved by embedding the power control information in the pilot symbols.
The aforementioned advantages of the present invention can also be achieved by embedding in the pilot symbols control information other than power control information. Moreover, the aforementioned technique of embedding control information in a channel evaluation signal (i.e., the pilot symbols) can also be advantageously applied in wireline communication systems as well as wireless ones.